Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of a muscle fiber, composed of actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other.

• Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force and movement.

• Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Contraction.

• Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

• Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

Muscle Groups and Functions

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and gluteals.

• Muscles Sectioning Cavities: Diaphragm separates thoracic and abdominal cavities.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle length remains the same (no movement, but tension increases).

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Sarcomere Substructures

• Z-line: Defines the boundaries of a sarcomere.

• A-band: Contains myosin filaments.

• I-band: Contains actin filaments.

• H-zone: Area with only myosin.

Function: Sarcomeres contract to shorten muscle fibers, producing movement.

Action Potential in Motor Neurons

• Initiation: Action potential generated by neurotransmitter (acetylcholine) release at neuromuscular junction.

• Propagation: Electrical impulse travels along the muscle membrane, triggering contraction.

Formula: $\Delta V = IR$ (Ohm's Law, relates voltage change to current and resistance in nerve conduction)

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product that must be expelled.

Respiratory System Structures

• Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, larynx.

• Lower Respiratory Tract: Includes trachea, bronchi, lungs.

Function: Upper tract filters, warms, and moistens air; lower tract conducts air to alveoli for gas exchange.

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Change Formula: $P_1V_1 = P_2V_2$ (Boyle's Law: pressure and volume are inversely related)

Intercostal Muscles

• Function: Assist in expanding and contracting the rib cage during breathing.

Blood Flow Through the Heart

• Oxygen-rich blood: Flows from lungs → left atrium → left ventricle → aorta → body.

• Oxygen-poor blood: Returns via veins → right atrium → right ventricle → lungs.

Respiratory Diseases and Disorders

• Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores bile.

• Pancreas: Produces digestive enzymes and hormones.